Network Rail was created in March 2002 to replace its failed private sector predecessor, Railtrack.
Network Rail took control of the nation's rail infrastructure in 2002
It has no shareholders but is run on a commercial basis.
Network Rail now controls the nation's railway infrastructure, including tracks, signals, most stations, tunnels and level crossings.
It is the successor to Railtrack, a private company which was placed in administration in October 2001 amid growing concerns over its safety record and heavy losses.
Private sector ownership of those assets had been judged a failure so the government set up a new structure that gave it much more control.
Railtrack's shareholders fought an unsuccessful legal battle for compensation, saying the Transport Secretary at the time, Stephen Byers had acted maliciously.
Network Rail does not have shareholders, instead it has a 100-strong oversight group.
Members come from rail operating companies, rail engineering firms and members of the public. It includes the Department of Transport.
They approve the appointment of directors and monitor their performance.
20,000 miles of track
1,000 signal boxes
40,000 bridges and tunnels
Operates 18 major stations
Carries 3m passengers per day
The board of directors has to operate within regulations set out by the Office of Rail Regulation, part of the Department of Transport.
Network Rail is a "not-for-dividend" company which means that all of its profits are invested in the railway network.
In the last financial year (which ended in March 2007) it reported profits of £1bn.
About half of its income comes directly from the government.
Most of the rest comes from rail operating companies which pay fees to use the tracks. But these fees are themselves set by the rail regulator at the behest of the government.
Additional income comes from its properties, including leasing space to shops at its stations.
Network Rail's official figures say that delays are down 28% since 2002.
It also says it has beaten its safety targets.
But the delays over Christmas and New Year have raised questions about its ability to maintain the network.
Since 2003 Network Rail has been taking over maintenance work from sub-contractors and has been building up its own engineering skills.
Its safety record was criticised after a fatal crash in February last year at Grayrigg, Cumbria.
An initial report blamed the crash on faulty points.